Performance Of Hybrid Supercapacitors And Nickel-zinc Batteries Based On Nickel-cobalt Compound-based Composites And Heterogeneous Material

With the spread and development of mobile electronics and electric vehicles,efficient and stable energy conversion and storage devices are urgently needed.Among various energy storage devices,aqueous and alkaline energy storage devices have been attracted much attentions due to their advantages from non-flammability and high ionic conductivity of electrolytes.Nickel-zinc（Ni-Zn）battery is a promising candidate for commercial applications owing to its merits of high voltage,high power,good safety,and low cost.However,nickel-based cathodes suffer from the issues of low electronic conductivity and poor reversibility,which cannot maximize the energy density of batteries.In addition,hybrid supercapacitor（HSC）is considered as an energy storage device integrating the high energy density of battery-type electrodes and the high power density of capacitive electrodes,which can better meet high demand of energy storage applications.Unfortunately,inadequate energy density limits its development.In order to solve the above problems,it is crucial to study high-performance battery-type electrode materials.Based on these,nickel-cobalt metal compounds are regulated and designed to construct a new electrode material,further improving electrochemical performance in Ni-Zn batteries and HSCs.The specific content can be divided into the following three parts:（1）A series of NiCo-S/RGO with different ratios of Ni to Coare synthesized using the method of precursor conversion.The effect of Ni/Cocomposition on electrochemical performance of NiCo-S/RGO is discussed.NiCo-S/RGO exhibits the best performance when the ratio of Ni to Cois 2:1.In addition,owing to RGO’s merit of high specific surface area,diffusion distance of electrolyte is shortened and reaction kinetics is enhanced.NiCo-S and RGO are combined to increase surface active sites,and RGO further improves the cyclic stability of NiCo-S,achieving excellent electrochemical performance of NiCo-S/RGO in Ni-Zn batteries.（2）The flake NiCoP-NiCoO₂/NiCo-PO_x heterojunction is prepared by hydrothermal treatment,annealing and phosphating treatment.The heterostructure is constituted by a great deal of high-crystallized NiCoP nanoparticles distributed in an amorphous NiCo?PO_xmatrix,and interfacial effect between separated materials with different chemical properties and crystalline phases significantly improves the electrochemical energy storage performance.Meanwhile,the effects of different degrees of phosphorization on components and electrochemical properties were studied.The NiCoP-NiCoO₂/NiCo?PO_xelectrode shows the best electrochemical performance when mass ratio of Ni_1.5Co_1.5O₄ to Na H₂PO₂?H₂O is 1:10.Then,HSCs and Ni-Zn batteries are assembled to evaluate their potential in practical applications,both of which demonstrate excellent energy density and high cycle stability.（3）NiCoP-x nanospheres with hollow structure are synthesized by spray pyrolysis and phosphating heat treatment,achieving excellent electrochemical performance.The special structure provides a large specific surface area,enhances interface effect between electrode and electrolyte,and provides a buffer for volume expansion during the electrochemical process,significantly improving electrochemical stability.In addition,the intrinsic low electronegativity of phosphating material greatly improves overall electronic conductivity and optimizes rate performance.At the same time,the effect of phosphating degree on composition and storage performance of NiCoP-x is studied.Hence,NiCoP-5shows best electrochemical performance in reversible capacity,rate performance and cycle stability,and exhibits great potential application in HSCs and Ni-Zn batteries.